Lyme Disease in Texas?
Enhancing Prevention Through the
Identification of Areas of Risk
Susan Swinson-Williams
GEOG 596A Capstone Proposal
Penn State MGIS Program
Advisor: Dr. Justine Blanford
Agenda
Overview
What is Lyme disease?
Lyme in Texas
Objectives
Methods
Anticipated Outcomes
Other Potential Applications
Timeline
Acknowledgements
References
Questions / Comments
Overview
• Many doctors believe that
“we don’t have Lyme in
Texas.”
• Many Texans travel out of
state for diagnosis and
treatment.
• Prevention and education are
the best approaches against
Lyme disease
• Prevention and education
efforts could improve if we
determined where humans
may be at greatest risk
What is Lyme disease?
• An infection caused by a corkscrew-shaped spirochete bacterium
• Most common vector-borne disease in U.S.A.
• Transmitted through bite of an infected tick
Darkfield microscopy photomicrograph, magnified
400x, of bacteria Borrelia burgdorferi (CDC, 1993).
Erythema migrans rash (Source: Wikipedia).
Dr. Burgdorfer, seen here inoculating ticks. Credit: NIAID/RML
Transmission and Distribution
•
Ticks are quite small, no bigger
than a pinhead in the larval and
nymphal stage
•
Their size enables them to feed
on hosts unnoticed
•
Three things necessary for Lyme
transmission:
•
•
•
the Lyme bacteria,
the ticks that can transmit the
bacteria,
the hosts that serve as a meal
for the ticks
Transmission and Distribution
The enzootic cycle of Borrelia burgdorferi (Source: Radolph, Caimano, Stevenson, & Hu, 2012).
Transmission and Distribution
Confirmed Lyme disease cases by month of disease onset in the United States from 2001-2010 (Source: CDC, 2013a).
Diagnosis and Quality of Life
Respondents reporting Fair or Poor health as a function of time until diagnosis (Source: Johnson et al., 2014).
Diagnosis and Quality of Life
Respondents reporting Fair or Poor health compared to the general population and patients with other chronic illnesses
(Source: Johnson et al., 2014).
Why Does Texas Need A Risk Map?
The few maps that exist on this subject are either
- Inaccurate or outdated
- not very specific
- or all of the above
Reported Cases 1990-2008
This 2012 ‘Risk Map’ doesn’t even show the entire USA nor correlate
with numbers of Lyme disease cases reported by the CDC. We can do
better than this, right? (Yale School of Public Health, 2012)
The CDC admits that approx. 90% of cases go unreported, so these figures are quite a bit
lower than reality. (LDA, 2012)
Why Does Texas Need A Risk Map?
Lyme continues to spread due to migratory animals, development, reforestation, and
climate change.
Multiple tick species exist in the U.S., some of
which have overlapping distributions.
Approximate distribution of three vector tick species in the U.S. (Source: Bakken et al., 2006).
Many animals serve as blood hosts for feeding ticks. (Source: Levy, 2013)
Lyme Disease in Texas
•
Previous research indicated that
1 to 4% ticks tested in every
public region of Texas were
infected with Borrelia
burgdorferi bacteria
(TXLDA, 2014).
•
Recent research, however, found
Borrelia infection in 45% of
Ixodes ticks collected from 20
counties in Texas and regions of
northeastern Mexico
(Feria-Arroyo et al., 2014).
Objectives
• Map prevalence of Lyme disease in Texas by:
– analyzing known distribution of reported human
cases in Texas
– survey of Texas residents with Lyme disease to
establish human incidence within the state.
Identify potential risk areas
through habitat mapping of
the vector.
Methods
To improve awareness of the prevalence of Lyme
disease in Texas
• Analyze existing reports from data reported to CDC (between 2002 – 2011)
to determine areas in Texas that have highest reporting/Lyme disease.
• Collect data via voluntary survey to determine current incidence of human
Lyme disease. Questions will include: illness length, co-infections,
diagnosis procedures, diagnosis was in state and other relevant data that
are HIPAA-compliant.
• Statistically significant areas of Lyme Disease will be identified using
Exploratory Spatial Data Analysis (e.g. GeoDa)
Methods
Identify potential risk areas
through habitat mapping of the vector
Tick Species
Geographic Location
Key Factors
Source
A. americanum
S Missouri, Texas
Forest, humidity, vegetation Brown et al., 2011; Texas A&M Agrilife
I.scapularis
N America
Negative association: urban, Glass et al., 1994.
wetlands, saturated soils
I.scapularis
Eastern USA, Maryland,
Wisconsin, Illinois,
Michigan,
Massachusetts,
Connecticut; Canada
Temperature, precipitation,
vapor pressure, land cover,
deciduous forest, leaf litter,
deer abundance, small
mammal richness and
abundance, canopy cover.
Extension, no date.
Brownstein, Holford, & Fish, 2005;
Brownstein, Holford, & Fish, 2003; DiukWasser et al., 2012; Githeko et al., 2000; Glass
et al., 1994; Guerra et al., 2002; Guerra,
Walker, & Kitron, 2001; Kitron, Bouseman, &
Jones, 1991; Kitron & Kazmierczak, 1997;
Lindenmayer et al., 1991; Moore et al., 2014;
Ogden et al., 2014;Roy-Dufresne et al., 2013;
State of Connecticut Department of Public
Health, 2013; Yang et al., 2010;Werden et al.,
2014
Methods – the NDVI
Normalized Difference Vegetation Index (NDVI) =
a ratio of near-infrared (NIR) to red light.
Healthy or dense vegetation =
high positive NDVI
Unhealthy or less dense vegetation =
lower positive NDVI
Water = negative NDVI
Methods
Identify potential risk areas
through habitat mapping of the vector
Vegetation Type
Satellite imagery (USGS GLOVIS) and the NDVI
(Normalized Difference Vegetation Index)
Land cover Type
National Land Cover Database (NLCD) (USGS)
Other Key Factors of
Tick Habitats
Temperature indices, rainfall indices, proximity to forest
edge, availability of hosts, human interface, etc.
Create a risk map
highlighting low to high risk areas
Anticipated Outcomes
• An updated map delineating the current extent of Lyme
disease incidence in Texas based on (i) tick habitats and
(ii) reported cases/survey.
• Create a risk map highlighting low to high risk areas
• Determine the correlation of Lyme disease with land
use/habitat.
• Provide recommendations
Other Potential Applications
Risk mapping can address Lyme in other neglected
regions both in the U.S. (Virginia, Georgia, Louisiana)
and other nations (Canada, Mexico, Caribbean,
Australia).
Similar techniques can address other vector-borne
diseases, which are the focus of the World Health
Organization’s 2014 theme.
– 1,000,000+ die from VBD per year. Many more
are left with chronic illness and disabilities .
– 50%+ of the world’s population is at risk. Travel,
trade and migration is increasing that number.
– Diseases also a serious impediment to poverty
reduction and socioeconomic development.
Timeline
Peer Review Presentation & Feedback
5/8/2014
Make suggested revisions based on peer feedback
Abstract Submission: URISA’s 52nd Annual Conference
5/15/2014
7/21/2014
Abstract Submission: TX Natural Resources Information System 27th annual
Texas GIS Forum 7/25/2014
Abstract Submission: ESRI Health GIS
Institutional
Review Board
(IRB) Training
8/1/2014
5/31/2014
Compile & Analyze Survey Results
Launch Survey
Statewide
8/6/2014
Final Draft & Advisor Review
6/4/2014
Apr
May
Jun
8/30/2014
Jul
Aug
5/19/2014
6/6/2014
Oct
Fall Term 1
Summer Term
Abstract
Submission:
Applied
Geography
Conference
Sep
Create potential
risk map based on
habitat data
Nov
Dec
Fall Term 2
2014
9/8 to 9/11/2014
Applied Geography Conference
10/15 to 10/17
TNRIS 27th annual Texas GIS Forum
10/20 to 10/24
URISA’s 7th Caribbean Conference
10/27 to 10/30
ESRI Health GIS
11/3 to 11/5
Acknowledgements
Very great appreciation to my advisor, Dr. Justine Blanford,
for her professional guidance, useful critiques, and patient assistance
in keeping my project focused and on schedule.
Also, special thanks to:
Anna E. Berman
Phyllis Shaw
Patricia Ricks
and the Texas Lyme Disease Association
Partial List of References
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Questions?
“It’s tick season
again!”